This invention relates to blower and filter apparatus for supplying clean air to a defined environment and more particularly to highly compact blower filter module arrangements configured on a unit volume basis which employ blower units having backward curved impellers.
Industrial and governmental requirements for clean room standards in many types of work environments have greatly increased. For example, in the electronics industry such diverse applications as the manufacture of magnetic hard disks, semiconductor integrated circuits, discrete electrical components, and various forms of electronic displays require clean room standards which to a large degree surpass those present in medical operating theatres. This has occurred because an occurrence as common as the presence of a single human hair, a substantial number of dust particles, or other common forms of airborne debris will frequently cause the self-destruction of the article manufactured. Therefore, it is of paramount importance that onerous clean room standards be imposed in environments of this type. Corresponding examples occur in the drug and pharmaceutical industry, in medical laboratories, and almost any form of application where airborne contamination is a problem due to the nature of the product or component being produced or utilized.
Since it is rare that entire facilities are provided with a decontaminated air supply, and even if it is, that the entire staff be required to wear clean room garb, the usual approach is to establish individual clean rooms and/or work stations meeting clean room requirements within selected manufacturing locations. In these clean rooms and at such work stations, the limited number of tasks requiring assembly or processing in a particle free environment are performed. The clean room will traditionally take the form of an enclosed space wherein all air introduced is filtered according to HEPA or ULPA standards. Similarly, independent work stations which may be employed in connection with a clean room or as an external work station are provided with a hood which effectively continuously imposes a laminar flow of filtered air about the assembly or processing location of the work station.
Because clean rooms, which are created after the fact, often have tight ceiling restrictions as do the work stations similarly created, it is important that the blower filter units employed to introduce purified air be compact in the height dimension. The ability to quickly and easily replace the filters of such units, on a periodic basis, is also important as is the ability to replace blower units which have failed. This occurs since down time associated with blower filter modules often results in disruption of the manufacturing or assembly operations taking place within the clean room and/or at the work station.
Typical clean room construction involves the creation of an enclosed volume defined by a number of walls, a floor, and a ceiling having blower filter modules arranged in the ceiling to create a continuous flow of clean air through the environment. This flow is frequently laminar in nature and exhaust ports may be provided to remove air from the room. Work stations employ similar blower filter units mounted in the hood above the work surface and differ from the clean room in that the work station is typically not enclosed. Clean air work stations within clean rooms may also be utilized to achieve improved results.
The blower filter units utilized generally take the form of a blower unit disposed to introduce air into a plenum formed between a blower unit and a filter which typically takes the form of a HEPA or ULPA filter. ULPA filters are capable of 99.9995% efficiency for particles of 0.12 microns and larger while HEPA filters are typically 99.99% efficient for particles of 0.3 microns and larger. The blower units are sized to provide ultraclean unidirectional air at class 10 (ULPA) or class 100 (HEPA) requirements.
Since a class 100 flow rate has the imposed requirement of 90 feet/min..+-. 10 feet/min at the output of the filter, it will be seen that the blower units employed are frequently quite substantial in size. This is particularly so since typical HEPA filters, for example, exhibit static pressures which can range from 0.5 inch to 1.3 inch water gauge. Thus, the blower unit must have sufficient operating power to create a pressure at the input to the filter to overcome the static pressure exhibited by the filter to achieve the requisite flow rate at the output side of the filter. For these reasons, it is not atypical that such blower units have power ratings which are quite substantial. This is particularly so where traditional forward curved impellers are employed since the same operate against a static pressure load and will overload the motor if that static pressure load is exceeded.
All blower units of this type have size and weight parameters which increase in a direct and non-linear fashion with respect to their power rating. As a result, the filter blower units tend to have a substantial height requirement, often exceeding 12 inches, and weight requirements which are incompatible with a simple hang mounting within a T-grid ceiling or the like. Accordingly, special height and support accommodations are often required especially where pre-filter arrangements are provided at the input to the blower unit.
The height and weight characterisitics of blower filter units of the type described often prove so onerous with respect to clean air installations having limited ceiling clearance and work station construction, that many approaches have been taken to lower the profile thereof. For example, motorized impellers have been employed to shrink the height dimension of the motor and in this way, fold the space required by a normal blower arrangement having an impeller connected to the extending shaft. Similarly, baffle arrangements have been employed in connection with the plenum so that the path of air flow from the impeller may also be folded. Such an approach is illustrated in U.S. Pat. No. 4,560,395 which issued on Dec. 24, 1985 to George P. Davis.
The use of a motorized impeller while clearly capable of reducing the space required by a more conventional motor impeller arrangement, in no way reduces the weight and size associated therewith since a relatively large motor must still be employed. Therefore, the height reduction, while substantial is limited.
Use of complex baffle arrangements are also disadvantageous since the presence, installation, and materials associated with these baffle arrangements increase the weight and cost of the resulting blower filter assembly and add difficulty to the maintenance thereof in cases where the blower unit must be replaced. In addition, complex baffle structures, no matter how precise, have the attendant difficulty that while the same may be optimized for a given blower filter combination, the characteristics of blowers and filters do not tend to be uniform. Therefore, while a selected baffle configuration may work quite well for a particular blower and filter in a particular unit, variations for a cross-section of manufactured units will cause substantial variations in performance. Thus, unless the baffle structure is optimized for each unit assembled, substantial operating variations on a unit to unit basis will result.
The present invention proceeds from a recognition that relatively low powered, light weight blower units chosen for a selected unit of volume or filter surface area may be employed to achieve low profile blower and filter apparatus for supplying clean air to a selected environment. The number of blower units within a given module is then determined as a function of the number of selected units of volume or the resulting filter surface area in the blower and filter module configured. In preferred embodiments, each blower unit employs a backward curved impeller which produces a radial air flow which pressurizes the plenum formed within the module configuration in a substantially uniform manner enabling a substantially laminar flow through a filter disposed perpendicular to the direction of air flow from the backward curved impeller without the use of baffles. Because the blower units selected are relatively small when compared to a single blower unit having a power rating corresponding to the sum of the smaller units utilized and no baffle structure is required, the height dimension of the resulting module is markedly reduced to achieve a low profile design. Further, since no baffle structure need be employed, optimum performance is acheived with all units despite normal variation in filter and motor blower parameters. In addition, marked cost reductions are acheived due to the absence of the baffle structures and resulting modules are relatively light weight so that no additional ceiling support structure is normally required.
Therefore, it is the principle object of the present invention to provide an improved low profile blower and filter apparatus for supplying clean air to selected environments. Various other objects and advantages of the present invention will become clear from the following detailed description of an exemplary embodiment thereof and the novel features will be particularly pointed out in conjunction with the claims appended hereto.